docs: def get(self, key):
      """Gets a value by a key.
  
      Args:
        key (str): Key to retrieve the value.
  
      Returns: Retrieved value.
      """
      self._create_file_if_none_exists()
      with open(self.filename, 'rb') as file_object:
        cache_pickle = pickle.load(file_object)
        val = cache_pickle.get(key, None)
        return val